This type of DC transducer with galvanic isolation are known for instance from DE 33 11 535 A1 or DE 20 2004 012 817 U1. A general problem with this type of AC rectifier switches is their energy requirement, which necessarily leads to a reduction in the output current. The primary current is transformed by a converter into an alternating current. This alternating current is transformed by a 1:1 transformer. The secondary current isolated galvanically from it is rectified. The entire switch must have very low loss, so that incoming and outgoing current are as close to equalized as possible. To reduce transformer losses, non-leaking single-aperture core transformers are used. Such transformers are, first of all, expensive. Secondly, single-aperture core transformers have a problem concerning high voltage tolerance, and it is impossible to correct bulk resistance or temperature influence.
The use of this type of DC transducers occurs especially in explosion-risk areas. In such areas, electrical systems galvanically isolated from the environment are found, such as sensors and actuators. The sensor signals can be current signals. As a rule, the sensor signal is a direct current. This direct current is the input current for the DC transducer. The input direct current should optimally be equal to the output direct current. This ideal situation cannot be achieved with conventional switches. Portions of the input current flow out in the form of parallel currents, transformer losses, or other loss currents over the entire switch. The sum of all loss currents is missing in the output current. To correct this, an additional current should be added to the output current. The state of the art sometimes makes use of auxiliary energy sources for this purpose.
DE 3139963 describes a switching device for galvanically isolated 1:1 transmission of a direct current signal. A measurement transformer is placed in the primary current circuit with a ticker, which produces an alternating current that is transmitted by a transducer to a rectifier. Here too an additional current source is provided. The DC transducer depicted in DE 2342294 also requires an additional current source in order to compensate for losses.